Posted
by
kdawson
on Wednesday December 19, 2007 @03:37AM
from the fire-came-by dept.

malachiorion writes "The Tunguska event, an explosion on June 30, 1908, cleared an 800-sq.-mi. swath of Siberian forest. Was it a UFO crash? An alien weapons test? Now, Sandia National Laboratories has released its own explanation for the Tunguska event. Using supercomputers to create a 3D simulation of the explosion, the Department of Energy-funded nuke lab has determined that Tunguska was, indeed, the explosion of a relatively small asteroid. The simulation videos are well worth checking out — they show a fireball slamming into the earth from the asteroid's air burst. The researchers caution that we should be keeping watch for many more small, potentially earth-impacting asteroids than we are currently tracking."

It seems that while the asteroid itself did not cause as much damage as previously believed (3-5 megatons vs 10-20), the asteroid was most likely much smaller than had been estimated. Too bad the article doesn't give some numbers about the size. Pretty scary thinking about one of these things hitting on top of or near a major population center.

Pretty scary thinking about one of these things hitting on top of or near a major population center.

Yes, every asteroid on television will undoubtedly hit over New York or Los Angeles. There must be some exceptionally high gravitational field at those locations.

Perhaps these dramatic presentations aren't really that helpful. It could be that volcanoes won't erupt under Los Angeles, ice hurricanes won't hit New York, and 10.0 earthquakes won't toss Los Angeles into the Pacific Ocean (and why isn't Chicago or London ever destroyed?). It might be helpful for you to calculate the area that the Tunguska Blast caused devastation, divide by the surface area of the earth, multiply it by the surface area of our major population centers, and then multiply it by the probability of this type of event occurring in the next 50 years. But this is boring and lacks the 'scary thinking' and drama, right?

Most hysterically, the government spent two weeks saying "No the movie is alarmist, this is all bollocks, etc". After that they turned around and said "Hey we are not committed to building a new Thames barrier" (they still have not got the brain to make it electricity generating, but brain and UK gov do not mix well).

I can't answer for Chicago, but London isn't in the States, and therefore the US media isn't really interested. For example, I don't remember War of the Worlds being set in America originally. That's not really a crack at the US media by the way, humans in general are more interested in things that happen close to home than thousands of miles away.

Remember the film 'Deep Impact', where the asteroid hit the Atlantic Ocean? We saw various people and locations in the States get wiped out. Then Morgan Freeman's voiceover [script-o-rama.com] said "blah blah, the wave hit Europe and Africa too, blah blah".

Téa Leoni gets to break the story and has a whole beach to herself with her father (what, nobody in the area got stoned enough to suicidally try and King Canute the wave back?) and two continents get a sentence...?!?!?!?!??

It might be helpful for you to calculate the area that the Tunguska Blast caused devastation, divide by the surface area of the earth, multiply it by the surface area of our major population centers, and then multiply it by the probability of this type of event occurring in the next 50 years. But this is boring and lacks the 'scary thinking' and drama, right?

What are you even implying? That your parent said "Wow, wouldn't it be cool if this hit a major population center"? It can happen, and it's getting increasingly more likely as we populate the world. The effects would be far greater than it hitting a big shrubbery, and thus it is more interesting to contemplate the aftermath, even from a purely scientific perspective due to e.g. the economic effects and to society.

Just chill down a little and don't be such a classic sociopath geek that assumes people are al

I'm speculating here, but I think density would be as important as mass for a smaller asteroid (I mean being solid lumps of hardy material, not the usual shale mix of rock and ice that might seperate out), provided it can last long enough to generate that single column of superheated plasma behind it. Something that might take out a city block on its own could wipe a city off the map if you added in the several mile long column of superheated gas that would impact shortly after, even if the asteroid itself

Would it really make a difference? Say it has a mass of 160,000 tons and impacts at 17 km/s, that's 5 MT of kinetic energy. It doesn't matter if it's made of tungsten or goose down. Almost all of that kinetic energy is going to be converted into blast and thermal energy.

Yes, but maybe it's because given an asteroid of a fixed size, mass is a function of its density and density is a function of its mass.

No.

It appears that most asteroids are conglomerates of shale, so they wouldn't be that dense, as in not that densely packed. That's why the idea of blasting them with nukes is a bad idea, they just seperate and reform later.

A closely packed cloud of shale hitting the atmosphere would be devastating, but not so much as a single cohesive mass. I don't know much about asteroid

It appears that most asteroids are conglomerates of shale, so they wouldn't be that dense, as in not that densely packed. That's why the idea of blasting them with nukes is a bad idea, they just seperate and reform later.

By reform I'm guessing that you mean reform via gravity? And since we are dealing with asteroids would it be safe to say that 'later' is later on an astrological time scale?

On that scale, I can live with a 'temporary' fix. (Live, have children, grow old, die, kids grow old...)

By reform I'm guessing that you mean reform via gravity? And since we are dealing with asteroids would it be safe to say that 'later' is later on an astrological time scale?On that scale, I can live with a 'temporary' fix. (Live, have children, grow old, die, kids grow old...)

Yes indeed, later could be a long time. However there would be no reason to try such a thing unless the asteroid were an immediate threat, in which case, unless your a fruit fly or something (what are those flies that hover over water?

What!? I don't know which planetary system you're from, mate, but since shale is a sedimentary rock (formed by compression of layers of mud, clay and silt beneath a body of water), none of the asteroids in this solar system are composed of it.

Some asteroids may be loosely bound accretions of smaller bodies, but we know for a fact that other asteroids (particularly the bigger ones in the belt) are big enough to melt and differentiate, with metallic c

because now with better computer simulations they can loft nice little toys into orbit that contain no nuclear matter, thereby not alerting any enviromentalist or anti-nukes, and have a very nice and clean weapon system.

I expect a lot more studies on the compositions of asteroids to determine just "which" kind is such a threat to us, which of course can lead to making these threats. All in the name of science.

would be that this is a weapons lab doing this sim. Now, we know roughly what size asteroid can do a LOAD of damage.

So what happens if a country creates a tug and then places it on the back of small asteroid, pushes to earth, and hits major cities? It would be seen as a natural disaster. In fact, if done right, the engines would burn up on the way down. No detection at all. And even the tugs heading out would likely not be detected. By hitting an enemy country with say 3 asteroids at 1x, and having another

I'm less concerned about a single city, which would be devastating but survivable.What scares me more was the (2004?) near-miss of an asteroid that could have hit somewhere in Pakistan or India precisely when they were in the middle of a very tense standoff. With immature command/control systems, what are the odds that would escalate into a nuclear shooting war, which would kill not the 10's or 100's of thousands of a single strike, but the 10's or 100's of MILLIONS of the resulting conflict.

Because of the additional energy transported toward the surface by the fireball, what scientists had thought to be an explosion between 10 and 20 megatons was more likely only three to five megatons. The physical size of the asteroid, says Boslough, depends upon its speed and whether it is porous or nonporous, icy or waterless, and other material characteristics.

Let's pick the middle ground and say four megatons, that's 1.67E16 joules. From what I can see, non-metallic asteroids really aren't all that dense because they tend to be very porous, and it seems likely that a metal asteroid wouldn't explode in this manner but would instead impact and bury itself. So call it 2600 kg/m^3. Assuming Earth escape velocity is probably a safe bet as well; it's possible the thing was an extra-solar object but not likely. So that's 11km/sec. Unless I'm screwing something up, I get a mass of 276,000,000 kg, and a spherical asteroid 30 meters in diameter.

I am on firm ground there? I mean, the only source of energy driving the explosion is the kinetic energy of the asteroid, it's just heating the thing up and making it go boom.

I've often wondered...how the populations (including the military) in some of the more... nervous areas of the globe would react to a suddden blinding light in the sky followed by an enormous blast wave.

I've often wondered how the populations (including the military) in some of the more... nervous areas of the globe would react to a suddden blinding light in the sky followed by an enormous blast wave.

Well the military wouldn't know who to attack, but you can be sure as hell someone would say "God did this because we made him angry by -insert reason here-"

For maximum effect, it should be a country with nuclear weapon technology (and means to deliver it) but not advanced enough to be able to discern (rapidly) between a nuclear blast (fission or fusion) and the impact of an asteroid. Also, possibly a country where it's important to keep appearances - leaders must be seen to be in charge, so they would react quicker than a thorough investigation would require. I can't think of many like that. North Korea maybe?

Nuclear weapons have a unique signature, which isn't present in conventional explosions. There are many spacecraft in orbit that have sensors designed to detect the atmospheric detonation of a nuclear weapon.

Those videos were really informative to me. I had always heard and read reports about how an "exploding" comet or asteroid had caused the devastation. But why and how would these things explode?! Well, they don't. But the all the momentum they transfer to the air creates a very devastating shock wave.

But the all the momentum they transfer to the air creates a very devastating shock wave.

The momentum was only part of the blast. The sudden heating from the release of lots of kinetic energy created an expanding blast fireball not unlike a nuke event. This was not just a sonic boom. This was a superheated fireball explosively expanding with a momentum toward the ground.

I'll grant you that they do not explode in the traditional TNT/explosives sense of the word. However, falling space debris can indeed "explode" when entering the atmosphere. As they push deeper and deeper and the air gets thicker, it presents more and more resistance on the falling object. Eventually, the wall of air becomes so dense that the action-reaction forces break the falling object up. Violently. Combine that with the fact that the asteroid/comet/meteor and surrounding air has been heated significan

You mean after the gigantic tsunamis die down? Well, once the rebuilding begins on a global scale, elevated precipitation will likely be the least of one's worries, especially if you live within 20 miles of the coast.

A 3-5 megaton blast over the Atlantic wouldn't cause so much as a rough surf advisory in Key West. In comparison, the USA built a 45 megaton bomb and the USSR's fission-fusion-fission Tsar Bomba would have been 100+ megatons had they not taken the sensible precaution of replacing the final fission stage with inert lead. If a mere 5 megaton warhead could cause such worldwide devastation, I'm pretty sure someone would have mentioned it before now (and trust me, I've read just about every far-fetched doomsday scenario imaginable.)

As for the possibility of similar-sized asteroid impacting the ocean instead of exploding above it--well, the article only says that the asteroid is now thought to be "only a fraction as large as previously published estimates". That doesn't tell us anything. The Tunguska asteroid may or may not have been large enough to trigger a tsunami had it impacted an ocean instead of exploding over land. I'm going to assume that an impact will usually be less energetic (though perhaps more concentrated) than a heat-induced explosion, in which case no, the Tunguska asteroid never posed a significant threat to the world as a whole.

That said, the Tunguska explosion is still fascinating as hell. I know that there's a lot of very strong evidence pointing to the asteroid theory, but it's still fun to toy with conspiracy theories. The atomic bomb was first being conceived of, Tesla's Wardenclyffe Tower was being tested (by some accounts, it was brought online the day before the explosion)... it's all absolute rubbish, to be frank, but it's very entertaining rubbish.

I'm currently reading Arthur C. Clarke's 'Rendezvous with Rama', which opens with the lines "Soon or later, it was bound to happen. On June 30, 1908, Moscow escaped destruction by three hours and four thousand kilometers -- a margin invisibly small by the standards of the universe."

In the book, we humans then go on to set up systems to track asteroids that may be a danger to earth, and set up defense systems against them. I know that we currently track some, but how well funded are these organizations that do this? This is really something that is quite important, as it is almost certainly just a matter of when, not if. Do we have systems in place that will allow us to destroy or divert any large asteroids that are determined to be on a path to impact with earth?

Actually 2 if you count the moon. Remember the huge number of craters that exist on the far side of the moon compared with the near side? I'm not saying all of those would've struck the earth, but we'd certainly be living in a different world if even a small percentage of them had struck.

The British MP Lembit Opik (name is Scandinavian) has attempted to draw attention to the seriousness of the problem. The media dismiss him as a crank. Watching him on television it has been apparent that television presenters and the like are bottomlessly ignorant on the subject, and because they can't admit it, they just seek to trivialise the issue.

OK, we shouldn't expect media people to know everything, but we are very poorly served by their almost total scientific ignorance. I suspect that politicians would have become interested in global warming much sooner were the mass media not so piss poor at explaining scientific issues to the public, and almost perversely proud of it.

To be fair, I don't think they treat him as a crank because of his views on asteroid defense. His choice (and treatment) of female companions ensures that he's regularly in the red tops for non-political reasons. I forget which of the fragrant Cheeky Girls he's stepping out with (see: http://en.wikipedia.org/wiki/Cheeky_girls [wikipedia.org]) now that he's dumped his previous TV weather forecaster fiancee, Siân Lloyd.

None of which should matter, or detract from his message, or make him appear any less sincere... It ju

it's difficult for the interviewers to engage seriously on a subject that he genuinely believes in

Which of course is a failing in the interviewer, not the interviewee. If he's there to talk about the threat from near-Earth objects and they start asking him about his personal life, that's down to them and their pandering to their gossip-hungry audiences.

The British MP Lembit Opik (name is Scandinavian) has attempted to draw attention to the seriousness of the problem. The media dismiss him as a crank.

I wonder why they do dismiss him? Global warming was the same. It seems curious in the face of the fact that the media, and the UK media in particular, spend most of their energy drumming up irrational abstract things to be afraid of (terrorists, pedophiles, etc etc), things which are unlikely to ever affect many in the UK.

This is good, but few people pay any attention to the other great danger beneath our feet: The earth's magma.

There are many supervolcanoes waiting to happen. With extreme volcanism, much of the life on earth can die. Some people have got the idea that a volcano can destroy an island or a small region, but few people realise that the whole planet (or more specifically its atmosphere, which is what we need most) is in danger of supervolcanoes, and that these phenomena happen from time to time (and we ha

The computer simulation is interesting, but the Tunguska event is unlikely to be an asteroid. There were strange events reported in the area for days prior to the explosion, there were odd lights, etc.

An alternative explanation was proposed by Wolfgang Kundt, a researcher at the Institut für Astrophysik, University of Bonn:

The basic proposal is that there was a natural gas leak, from the Earth. The gas rose to a certain height, then drifted downwind. After several days, a lightning strike ignited the airborne gas, and the flame then traveled along line (of drifted gas), to the ground source.

It is worth reading the article. An asteroid impact is sexy, but the alternative explanation fits with the data much better.

It is worth reading the article. An asteroid impact is sexy, but the alternative explanation fits with the data much better.
And how does a natural gas explosion leave the nickel and iridium deposits that were found at the site? An asteroid impact is not the accepted theory because it is "sexier", but because of Occam's razor.

Expeditions sent to the area in the 1950s and 1960s did find microscopic glass spheres in siftings of the soil. Chemical analysis showed that the spheres contained high proportions of nickel and iridium, which are found in high concentrations in meteorites, and indicated that they were of extraterrestrial origin.

I've seen the 'natural gas' theory before. It's so contrived that it's almost like science-comedy.

The points raised by the paper you linked to which I found compelling were. ..

1. That there have been far more events in recorded history similar to Tunguska which have been volcanic or geologic in nature than have been due to cometary impact, raising the question of probabilities. --Mt. Saint Helens blowing its top in 1980 is an example, as was Krakatoa in 1983. There was also the 1986 limnic eruption of 1.6 million tonnes of CO2 from Lake Nyos which suffocated 1,800 people in a 20 mile radius. Sometim

1. That there have been far more events in recorded history similar to Tunguska which have been volcanic or geologic in nature... Mt. Saint Helens... Krakatoa... Lake Nyos... And which of these are examples of the supposed megaton range methane gas explosions? Why... none of them. Sorry, unrelated geophysical events don't provide any precedent for the proposed mechanism. The notion seems a bit difficult to buy into - the explosive limits for methane in air is usually quot

What strikes me (excuse the pun) is that now they've determined it was an asteroid the attitude is "oh well these things happen - at least it wasn't someones big secret weapon".Ok, so let me ask, whats the difference?

If it was a big super weapon like a Nuke everyone would be panic strikken. Because it was just a asteroid there is no reason to worry. Lets not forget that large enough asteroids could wipe out the entire planet (not just one or 2 countries like our nukes..)

The new simulation which more closely matches the widely known facts of destruction than earlier models shows that the center of mass of an asteroid exploding above the ground is transported downward at speeds faster than sound. It takes the form of a high-temperature jet of expanding gas called a fireball.

The theory I've heard a few times was that it was anti-matter. Doctor Raymond Stanz, however, postulated that it may have been the result of a dimensional crossover. This theory has not been widely accepted, though, because no P.K. readings have been captured to support this claim.

Free American English Lesson: Adverbs modify verbs.
Verb in the Subject Sentence: Missed (past tense)
Context: This asteroid was very near to Earth when it missed us.
Adjective: Near (adverb form: nearly)
Thus: The asteroid nearly missed Earth.

Would there be any chance of a small asteroid (one that could cause some problems) currently heading for earth not be detected yet by scientists?

Yes. There is a very real chance that a chunk of rock the size of a basketball court could come at us tomorrow. A very very small, but very real chance. Asteroids that come from the sunward side of Earth's orbit are harder to detect because they are obscured by the Sun. One could come from that direction and astronomers may never see it. Most of the meteors that streak across the night sky are space stones no bigger than your hand, and usually about the size of a pea or smaller. Larger ones come down, but very infrequently. It is impossible for astronomers to chart, track or project the trajectories of the billions of space rocks left over from the formation of the Solar System.

Imagine a world where a small asteroid fragment or comet had struck Russia 60 years after Tunguska - during the depths of the Cold War. It would be a very different world today indeed.